Control system for paper machine drives



July 20, 1948. R, R, BAKER AL 2,445,416

CONTROL SYSTEM FOR PAPER MACHINE DRIVES Filed Feb. 22, 1945 2 Sheets-Sheet 1 m Ma" ATTORNEY y 20, 1948' R. R. BAKER ETAL 2,445,416

CONTROL SYSTEIFOR PAPER MACHINE DRIVES Filed Feb. 22, 1945 2 Sheets-Sheet 2 WITNESSES:

64 E he INVENTOR$ as "Ba/(erana 7 87/ w /m-E. f/arr/s.

CuJ -fl ka y Ms. M

y ATTORNEY .Patented July 20, 1948 CONTROL SYSTEM FOR PAPER MACHINE DRIVES Best 8. Baker, Swisavale, and Walter R. Harris, Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 22, 1945. Serial No. 579,254

(fill. 92-44) 6 Claims. 1

Our invention relates to paper machines in which a sheet of paper is initially formed on the surface of a traveling foraminous carrier such as a Fourdrinier wire screen.

The foraminous carrier or screen of such machines forms, as a rule, an endless band which travels from a breast roll to a couch roll, the latter being usually driven from the line shaft of the machine; The wet paper stock is charged onto the screen near the breast roll and is dried while on its way towards the couch roll, in order to attain the required consistency and strength before it leaves the screen at the couch roll prior to passing through the subsequent sections of the machine including, for instance, presses, calenders and driers.

It has been found favorable to provide such paper machines with an auxiliary couch roll between .the breast roll and the main couch roll and to place a suction box inside the auxiliary roll to remove water from the paper stock.

Our invention, more specifically, refers to paper machines having an auxiliary couch roll of the just-mentioned type and consists in improvements relatin to the drive and control of the auxiliary couch roll relative to the operation of the main couch roll drive.

It is an object of the invention to provide a paper machine in which the drive of the auxiliary couch roll is so controlled as to reduce or prevent the occurrence of slippage between the auxiliary couch roll and the traveling foraminous carrier, thereby eliminating excessive'wear of the carrier and contributing to-a smooth operation of the Fourdrinier section of the machine.

It is also an object of the invention to provide an auxiliary drive for the Fourdrinier wire which will be so controlled as to not only provide the required driving effort of the auxiliary roll. but also to relieve to an optimum degree the main couch roll drive of driving eil'ort and thus reduce or prevent the occurrence of slippage between the "main couch roll and the Fourdrinier wire.

The invention aims also at obtaining a torque control of the auxiliary couch roll drive in such a manner as to limit the power transfer between auxiliary couch roll and Fourdrinier wire screen in dependence upon the degree of vacuum in the suction box of the auxiliary couch roll.

Another object of our invention in conjunction with the foregoing is to provide a. separately driven auxiliary couch roll whose speed of rotation is automatically kept within desirable limits in proportion to the speed of the main couch roll drive, and which is controlled to develop a 2 torque within the capacity of the surface portion or are of contact of the auxiliary couch roll with the foraminous carrier and/or in accordance with the pressure exerted on the auxiliary roll by the charged foraminous carrier.

A still further object, subsidiary to the one last mentioned, is to provide the drive of an auxiliary couch roll with a torque control which operates in dependence upon the degree of pressure of a suction box disposed within the auxiliary roll so that an increase in vacuum and hence an increased pressure of the f-oraminous carrier against the roll surface is met by an increased torque of the auxiliary couch roll motor thus providing increased capacity for power transmission of the auxiliary roll.

It is also an object of our invention to devise a paper machine drive, as set forth hereinbefore, in such a manner that the desired speed and torque control is efiected without the use of contactors and the like circuit interrupting devices in the main control circuit, so as to achieve a continuous and gradual control operation over the entire intended range of control.

Our invention aims also at providing an auxiliary couch roll drive, speed and torque controlled in accordance with the foregoing objects, that is automatically rendered inoperative when the main couch roll drive is disengaged and when the Fourdrinier section has decelerated below a given minimum speed, thereby providing a, cutoil effect with a delay correspondin approximately to the deceleration characteristic of the Fourdrinier section in order to prevent overstress on the carrier during stopping periods.

The foregoing objects and the means provided by our invention for achieving the desired results will be understood from the following description of the embodiment exemplified by the drawing in which Figure 1 represents diagrammatically the webforming section of a paper machine together with a control system according to the invention,

Fig. 2 is a modified form of part of the system according to Fig. 1, and

Fig. 3 represents diagrammatically another embodiment of a paper machine control designed and operative in accordance with the invention.

In order to facilitate comparing the different embodiments with one another. the last two digits of the reference numerals applied to Figs. 2 and 3 are identical with the respective reference numerals of Fig. l wherever similar or similarly functioning elements are designated thereby.

Referring to Fig. 1, the wet section of the illustrated machinery comprises a MC and a breast roll BC with anauxiliary couch roll AC located between them. An endless i'oraminous element such as a l'ourdrinier wire screen I engages the rolls BC. AC. and MC and is guided along its path of motion by one or the several guide rolls such as the one denoted by numerall. Anumberoisuctlonboxeslarelocated adjacent the traveling carrier i in order to remove water from the wet paper stock or pulp entrained bythe wire screen. Another suction box 4 is located immediately adjacent to the auxiliary couch roll AC and preferably. as shown.

of the machine, ior instance. through the press indicated at I.

The traveling motion is imparud to the wire screenibyamaindrivewhichactsuponthe main couch roll MC. To this end. the M ll of roll EC is connected by a bevel gearing Ii with an intermediate shaft II. A coupling I! servestoconnectthisshaitwithaconepulley it which is driven by a belt II from a cone pulley II on the line shaft LB oi the machine. The line'shait LB extends along the paper machine and serves also for driving other sections such as roll presses, calenders. and the like devices. A motor 1M of adjustable speed, consisting of any available source of motoric power such as a steam engine or other prime mover or an electric motor, serves to drive the line shaft 18. The coupling II is provided with a manual control lever il associated with an electric contact device II. The contact at II is closed only when the coupling II is clutched in and, hence. when the drive or the main couch roll MC in operation.

An auxiliary or helper drive acting on the auxiliary couch roll AC is provided for imparting thereto a positive motion in the direction oi travel or the wire screen I. This helper drive is of the variable voltage type and comprises a direct current motor All in connection with a main generator MG. A shaft I. or other suitable mechanical transmission connects the armature II of motor All with the auxiliary couch roll AC. The neld winding I! of motor All is energized through an adjusting or calibrating rheostat ll from the mains x and Y oi an exciter generator I! which supplies direct current of constant voltage. This exciter torms part of a motor generator set which includes also the above-mentioned main generator MG and has a common shalt II driven by a constant speed motor CH. The armature ll of the exciter I! has its output terminals connected to the above-mentioned mains X and Y. A shunt held winding 82. energisedrrommainsxandYthroughanadjusting or calibrating rheostat ll. provides sell-excitation. It will be understood that a shunt held windingmaybeusedinsteadotorinaddition to the shunt neld winding It. or that any other suitable source of constant direct current voltage may be employed for energizing the control sys- The armature oi themain'gsncatorllb is series connected with the armature Ii oi motor All through a resistor which serves as a meteringdeviceiorapurposetobedescribedinalater place. The main generator KG has two cumulatively acting neld windings l! and ll. These two ileld windings are supplied with direct current excitation which. is varied in dependence uponthespeedotthemaincouchrollllcand also in dependence upon the torque requirements or the auxiliary couch roll AC as imposed thereon by the wire screen I and paper stock under the eiiect oi the suction means. In order to achieve such a combined control and in accordance with the objects oi the invention. a combined system oi control generators is employed which comprises a regulating generator RC and a pilot exciter PI in conjunction with a bridge type control network BR. interconnecting these two generators and providing the ileld excitation for the main generator H0.

The regulating generator 8.8 has its armature I mounted on the shaft 8. A self-excited tield winding It is series connected with the armature ll through an adjusting or calibrating rheostat II and the diagonal branch A-B oi the bridge circuit BE. A second held winding ll of the regulating generator. hereinafter called the control iield winding, is connected across the metering resistor II and hence is excited by a voltage which varies in proportion to the current supplied by the main generator M0 to the drive motor AM. Another held winding ll of generator R0, hereinafter called the pattern held winding. is excited from the exciter mains x and Y through a rheostat mechanism PR whose design and operation will be described hereinafter. The

control held winding l8 and the pattern iield winding it set diilerentially with respect to each other; that is. their resultant field eilect on the armature of the regulating generator R0 is substantially zero when the current supplied by the main generator M0 to the drive motor All is in accordance with a value of excitation imposed on the pattern iield winding ll by the rheostat mechanism PR.

The self-energizing ileld winding II has the resistance of its circuit adjusted so that the resistance line is approximately coincident with the no load saturation curve. with this adjustment. the self-energizing ileld will furnish the major portion 0! the magnetomotive force necessary to .nelds under normal contltions. Bince. as mentioned. the control field produced by winding I8 and the pattern field produced by winding it are normally balanced when the upper current is flowing in the circuit oi the auxiliary couch roll motor, the regulating generator RB has the eliect or compensating the voltage of the main generator MG so as to maintain an armature current in the drive motor AM in accordance with the setting or the rheostat mechanism PR.

The pilot exciter P! has its armature Ii driven by the intermediate drive shai't It. The lleld winding ll oi generator PI: is energised from the exciter mains x and Y through an adjusting rheostat I. Since this excitation remains constant. the output voltage of generator PI: varies in proportion to the speed of the main couch roll MC. This voltage is imposed on the second diagonal branch C-D oi the bridge circuit 88. The two held windings I and II or the main generator MG are disposed in two opposite legs oi the bridge circuit, while the remaining two legs are formed by resistors OI. and II. These four legs of the bridge circuit are balanced. Consequently, the current from the pilot exciter PE flowing through the bridge causes no voltage drop across the terminals -AB to which the mulleting generator RG is connected. Similarly, the current flowing from theregulating generator RG through the bnidge causes no voltage drop across the terminals C-D to which the Pilot exciter PE is co The tiometrlc rheostat mechanism PR is actuated by a'diaphragm motor DR. The housing or this motor is connected by a conduit 80 with the suction box I of the auxiliary couch roll AG and contains a spring biased diaphragm I which is deflected in opposition to the force of its spring in accordance with the magnitude of the vacuum effective in the suction box 4. Diaphragm motors of this type are available in difi'erent constructions and are not part of the present': invention proper since any suitable pressure responsive actuating device may be used. A movable link it. is connected with the diaphragm at so as to be moved vertically in accordance with a diaphragm deflection. The link I! cooperates with two sets .3 and N of leaf springs which at one extremity are firmly attached to a rigid insulating carrier. While the other end or each leaf spring carries a contact. The leaf springs or both sets 83 and it are electrically connected to a corresponding number or steps of two resisters 85 and 08, respectively. When the actuating link 82 is moved upwardly. it will cause the leaf springs of set ll to contact each other progressively, thereby short-circuiting a progremng number of steps 01' resistor 88 and reducing the effective total resistance of resistor 85. Similarly, when the actuating link 82 moves downwardly, it will cause the leaf springs or set N to short circuit a progressive number of steps of resistors It.

Rheostat mechanisms oi the just mentioned leaf spring type are known and are more fully described in U. S. Patent 2,249,826 to C. R. Hanna. It will be understood, however, that the use or this particular type of potentiometric device is not essential to the present invention and that, if desired, other type devices may be used instead.

The midpoint between resistors II and II is connected with one terminal of the above-mentioned pattern field winding 54. The remaining terminal or resistor It is connected through an adjusting rheostat 81 with exciter main Y and hence with the other terminal of the pattern field winding II. The remaining terminal of resistor I! is connected through another adjusting rheostat at with exciter main X through the contact 18 of a control relay CR whose relay coil 11 is controlled by the contact IQ of a timing relay TR. The main operating coil 01 the timing relay is denoted by 13, while numeral 14 represents a neutralizing coil which is separately excited through an adjusting rheostat 15. This rheostat me control system is in operative condition after the constant speed motor CM has assumed its normal speed or rotatio When the clutch it is engaged by actuating the lever ll, the main couch roll MC and the l 'ourdrinier section or the machine are driven at a speed determined by that or the line shaft motor LM. The clutch contact ll closes the circuit 0! coil 13 oi the timing relay TR so that the appertaining contact II is closed. This establishes an energizing circuit for coil 11 and hence causes the control relay CR to close its contact 10. As a result, the resistors 85 and 86 of the rheostat mechanism PR are now connected with the exciter mains X and Y for energizing the pattern field winding N. The pattern field causes the regulating generator RG to supply energiza'tion to the generator fields l! and 43. As a result the motor AM of the auxilia y couch roll AC is energized so as to develop a torque which corresponds to the setting or the vacuum controlled rheostat mechanism. With an increase in vacuum, the actuating member I! o! the diaphragm motor DR will move upwardly.

thus reducing the eflective total resistance or reslstor It and increases the eiiective total resistance oi resistor 8'. This increases the voltage across the pattern field N. Consequently, the current supplied by the main generator MG to the drive motor AM is also increased. In this manner, an increased vacuum is accompanied by an increase in torque 01' motor AM. Similarly. when the vacuum in suction box 4 decreases, the actuating member '1 of the diaphragm motor DR is lowered, thereby reducing the eilective total resistance of resistor 06 and increasing the eflective total resistance of resistor II and decreasing the excitatlon of winding It and hence the current and torque of the drive motor AM. The minimum load obtainable at increasing vacuum is determined by the setting or resistor l1. while similarly the maximum load to be imposed on motor AM at increasing vacuum is determined by the setting of resistor I8.

permits selecting. between limits. the timing period oi the relay. The control system contains also a voltage relay VR whose coil 1| is connected across the armature ii of the pilot exciter PE and responds to a given minimum voltage and hence to a corresponding minimum speed of the main couch roll drive. The contact 12 of the voltage relay VR is interconnected with the control relay-CR and the coupling contact i8.

When during the initial stage oi operation the wire screen accelerates or when the speed range 0! the Fourdrinier section is adjusted over the available operating range, the pilot exciter PE will synchronize the operating speed of the auxiliary drive motor AM with that or the main couch roll MC. At the same time, the regulating generator RG applies the necessary compensation to the field of the power supplying generator MG to hold the driving torque of motor AM at the proper value in accordance with the above described setting and operation of the vacuum controlled regulating means.

' When at the end of an operating period the clutch I3 is disengaged, the contact I! is immediately interrupted while the Foul'drinier section of the machine starts decelerating. It is desirable to maintain the motor AM energized in such a. manner that it also continues running at a gradually decreasing speed matching the declining speed of the main couch roll until the Fourdrinier section is substantially at rest. The above mentioned voltage relay VR and the timing relay TR serves to accomplish this result. Alter the machine.

celerated by a starting generator.

7 and opens its contact I2. This inte rupts the circuit oi the main coil It oi the timing relay TR; so that contact ll oi relay Tit will be opened. However, this occurs only ai'ter the elapae oi the timing period adjusted by means oi the rheostat ll.

operating period oi the paper machine but also at accelerating and decelerating speeds as well as during speed changes oi the main couch roll drive.

Another advantage oi a control system according to the invention is the iact that the auxiliary drive motor and the appertaining main generator are permanently connected so that no contactors are required in the main power circuit. The operation oi the system is entirely automatic. It will start, stop and change speeds in relative synchronism with the main couch roll without requiring any attention irom the attendant. At the same time, the driving eiiort oi the auxiliary couch roll motor is automatically adjusted to provide a torque in correspondence with the vacuum in the suction box and hence with the load and torque requirements oi the auxiliary couch roll.

While the above described embodiment oi Fig. l is especially designed ior paper machines in l armature Ilioi a pilot exciter PI. The appertaining exciter fleld winding is denoted by Ill. The above-mentioned starting and running generators supply power to a variable voltage bus PB. The main couch motor ms has its armature oi the main drive eiiected by the closure oi coupling It inFlg. 1. Switch 8 according toIig. Sis provided with an interlock contact III, which. as regards its function. corresponds to the elements l1 and it ln-the system shown The exciter mains X and Y represented as well as the voltage relay V8 with its coil and contact iii are shnilar to the respective ments oi Fig. 1 and periorm substantially ele the

go same iunction. Assuming the power bus P8 in the modification oi Fig. 2 to be energised. the closure oi switch 8 causes the motor ms to start operating the main couch roll MC and energizea a timing relay (not shown in Pig. 2) which. as in the embodiment oi Fig. 1, causes a control relay to place the regulating generator set in operating condition. When the main motor NH reaches suflicient speed. the corresponding increase in output voltage oi the pilot exciter PI which the main couch roll is driven mechanically irom a line shaft, it should be understood that our invention is likewise applicable to other kinds oi drives, ior instance. to the so-called sectional electric drives in which a separate electric motor is used ior operating the diiierent sections oi The individual drive motors are supplied with power irom a common main generator and the various sections are started and ac- Bpecial control means are provided to transier from the starting generator to the main or running generator when the operating speed is reached. In this manner, each section is usually started and acceleratedindependently oi the other sections.

The modifications of our invention represented .by Figs. 2 and 3 serve to illustrate two diiierent applications at our control system to sectional electric drives oi the type just mentioned.

The modification illustrated in Fig. 2 concerns only the portion oi the control system associated with the drives oi the main couch roll and auxiliary couch roll. Thereiore. only this portion oi the system is illustrated in Fig. 2, all other elements oi the complete system being similar to the corresponding parts as shown in Fig. 1 and described in the ioregoing.

According to Fig. 2, the auxiliary couch roll AC whose suction box is connected by a conduit III with a diaphragm motor is driven by an auxiliary motor AM whose armature and ileld winding are denoted by "I and II! respectively. The armature "I is energised by a main generator (not shown in Pig. 2) which corresponds to the generator M0 in Fig. 1 and is shaited together with a regulating generator and exciter. The main couch roll MC according to Fig. 2 is driven by an electric motor MM whose shait drives also the causes the voltage relay to close its contact 212. The iurther operation or the system is the same as that described previously in conjunction with Fig. 1.

In the embodiment shown in Flg. 8. the laurdrinier wire ill passes over a main couch roll MC and an auxiliary couch roll AC which contains a suction box Ill connected by a conduit ill with a diaphragm motor DR. for controlling a rheoatat device PR. substantially in the manner described above in conjunction with Fig. 1. The main couch roll MC is driven by a main motor ms and the auxiliary roll AC is driven by a separate motor AM. Motor All has two cumulatively acting control iields I22 and m. The main motor Ill receives constant field excitation. Both motors are energised by adjustable voltage irom a starting generator 86 or a running generator 00 depending upon which of the contacts 800 and ill is closed. While these contacts are schematically illustrated as kniie switches, it will be understood that they consist usually oi a control device designed to secure the proper sequence oi operation. The armature circuits oi motors MM and All extend through a switch I which is mechanically coupled with an interlock contact Iv ior controlling the operation oi a voltage relay VR and a timing relay TR. The coil I'll oi relay VB is connected across the armature oi motor All. Thecontactfl! oirelayVRliesinparallelto the interlock contact ill ior controlling the energization oi the control coil I'll oi a timing relay TR whose contact is denoted by I'll. llxcitaflon ior coil I" is supplied by the mains X and Y oi an exciter generator xx. A control relay CR. has its coil ill connected between the exciter mains I and Y under control by the relay contact I" and p rates two contacts "I and ill.

' The exciter xx has its armature mounted on the shait oi a regulating generator R6 which is drivenbyaconstantspeedmotorcll. The armature Ill oi regulating generator is acted upon by a self-excited field winding "I. a control neld winding I" and a pattern iield winding I. windings ll! and! operate diii'erentially with respecttoeachother,a'ndtheseli-excitingwind- 9 ing 352 has its circuit so ratedthat its resistance line is approximately coincident with the no load saturation curve of the generator.

The armature 3H of generator R is connected acrossthe terminal points A and B of a bridge circuit BR. The two other diagonal points C and D of circuit BR receive constant excitation from the exciter mains X and Y. The four bridge branches are formed by two resistors 360 and 310 and by the above-mentioned field. windings 322 and 323 or motor AM. when the operation of the system is started, a contact 393 is closed, thereby also closing the interlock contact 333. Then the contact "I is closed,- thereby energizing both parallel connected motors MM and AM by power supplied by the starting generator SG. At a later time, when the motors have sufliciently accelerated, contact 390 is closed and contact 39l opened so that the further operation is performed under power supplied from generator GG. When contact 393 closes, the interlock contact 394 applies voltage to coil 313 so that the timing relay TR picks up and energizes coil 39! oi. control relay CR which then closes its contacts 393 and 331, thereby placing the regulating generator set into operative condition. The voltage generated in the armature 33l oi generator RG is then controlled in dependence upon the excitation oi the pattern field 354 and the oppositely acting excitation of the-control field 353. The pattern field excitation depends on the operation of the rheostat device PR, and hence is governed by the degree of vacuum in the suction box 303 while the control field 333 is excited in accordance with the load current in the armature circuit of motor AM measured by a resistor 3. Consequently, the resultant field windings 333 and 354 is substantially zero when the current supplied to the motor AM is in accordance with, the excitation imposed on the pattern field winding 353 by the vacuum controlled rheostat mechanism PR. The bridge circuit BR contains the two field windings I 322 and- 323 of motor AM in opposite bridge branches and operates in a manner similar to the function of the bridge circuit described previously in conjunction with Fig. 1, except that the control eflect is not imposed on the field or a generator but acts directly on the field of the drive motor AM. As a result, the driving torque of motor AM is maintained at the proper value in accordance with the vacuum pressure measured by the diaphragm motor DR. When the supply of current to the two motors AM and MM is interrupted in order to stop the machine, the voltage relay VR will not be deenergized until the speed drops to a given low value after which the timing period of relay TR becomes effective before removing the regulatinggenerator RG from the control fields 322 and 323 of the motor AM. In this manner the system automatically takes care of maintaining its control .iunction during decelerating periods in accordance with the inertia characteristics of the machine section.

It will be obvious to those skilled in the art that control systems according to the invention may be modified as to details without departing from the gist and spirit of this disclosure. We, therefore, wish this specification to be understood as illustrative rather than in a limiting sense.

We claim as our invention:

1. In a paper machine, the combination of a paper-forming, travelling foraminous member, a main couch roll engaged by said member, a main drive for driving said main roll, an auxiliary couch roll engaging said member ahead of said 10 main roll in the direction of travel, suction means disposed adjacent said member and close to said auxiliary roll, a motor in driving connection with said auxiliary roll, a main generator connected with said motor for supplying energization thereto and having field means for varying said energization, a pilot generator mechanically connected with saidmain drive and electrically connected to said field means so as to excite said main generator for operating said motor at a speed approximately proportional to that of said main drive, and control means also connected to said field means for superimposing on said motor a torque control in accordance with the operation 01' said suction means, said control means comprising a control generator having an armature circuit connected with said field means and two differential field windings for controlling the voltage of said circuit, one of said windings being connected with said main generator so as to be excited in dependence upon the energizetion supplied to said motor, a source of controllable voltage connected to said other winding,

and a pressure responsive control device disposed between said suction means and said voltage source iorcontrolling the latter in accordance with changes in vacuum of said suction means so as to cause an increase in torque of said motor in dependence upon a decrease in vacuum pressure,

2. In a paper machine. the combination of a paper-forming, travelling ioraminous member, a main couch roll engaged by said member, a main drive for driving said main roll, an auxiliary couch roll engaging said member ahead or said main roll in the direction of travel, suction means disposed adjacent said member and close to said auxiliary roll, a motor in driving connection with said auxiliary roll, a main generator connected with said motor for supplying energization thereto and having field means for varying said energization, a bridge-type circuit arrangement having two diagonal branches and including said field means outside of said diagonal branches so as to energize said field means in dependence upon the voltage across said diagonal branches, a pilot generator disposed to be driven in accordance with the speed of said main drive and connected across one of said diagonal branches to impress thereon a voltage proportional to said speed, a control generator having an output circult connected across said other branch to impress another voltage thereon and having two diil'erential field windings for controlling said other voltage, one of said windings being connected with said main generator so as to be excited in dependence upon the energization supplied to said motor, a source of controllable voltage connected to said other winding, and a pressure responsive control device connected between said suction means and said voltage source for controlling the latter in accordance with changes in vacuum oi said suction means so as to cause said motor to increase its torque at decreasing vacuum pressure.

3. In a paper machine, the combination of a paper-forming, travelling foraminous member, a main couch roll and a breast roll engaging said member and being spaced from each other so as to lie substantially at the end and beginning respectively of the paper-forming portion of said member when in operation, a main drive for driving said main roll, an auxiliary couch roll engaging said member between said couch roll and breast roll, a suction box disposed within said auxiliary couch roll and adjacent said member, a motor in driving connection with said auxiliary roll. a main generator connected with said motor for supplying energization thereto and having field means for varying said energiaation. a bridge type circuit having two diagonal branches and including said field means outside 0! said diagonal branches so as to energize said field means in dependence upon the voltages across said diagonal branches. a pilot generator operative in accordancewiththespeedoisaidmaindriveand connected across one or said diagonal branches to impress thereon a voltage substantially pr r. tional to said speed. a control generator having an output circuit connected across said other branch to impress another voltage thereon and having two diii'erential field windings for controlling said latter voltage. one oi said windings being connected with said main generator so as to be excited in dependence upon the margintion supplied to said motor. a source of controllable voltage connected to said other winding. and a manometric control device hydraulically connected to said suction means and electrically connected to said source for controlling the latter in accordance with changes in vacuum of said suetionboxsoastoincreasethetorqueoisaid motor at decreasing vacuum pressure in said suction box.

4. An electric drive for the suction section of a paper machine. comprising a main mil drive. a direct-current helper drive motor having a separately excited field winding and an armature. a main generator having an armature electrically connected to said motor armature for providing controllable voltage therefor and having separately excited field means for controlling said voltage, a pilot generator having means for connecting it to said main drive and being electrically connected to said field means ior causing said voltage to vary in dependence upon the speed oi said main drive. a regulating generator having an armature connected to said field means for superimposing a regulating eil'ect on said voltage and having a control field winding for controlling said regulating efi'ect. an auxiliary motor mechanically connected to said armatures c! said main generator and said regulating generator for operating them at substantially eondant speed. and a control device responsiv to auction vacuum and electrically connected to said controifieldwindingsoastocauseanincreasein torque of said direct-current motor in dependence upon a decrease in vacuum.

5. An electric drive for suction section of a paper machine. comprising a main roll drive. a direct-current helper drive motor. a main generator having an armature series-connected with said helper drive motor and being controlled in dependence upon the speed of said main roll drive to provide for said helper drive motor a voltage variable in dependence upon said speed. said main generator having field means for imposing a regulation on said voltage. a regulating generator having an armature connected to said field means and having two control field windhills of difierential action relative to each other. oneoisaidcontrolfieldwindingsbeingconnected to said main generator and said helper drive motorsoastobeexcitedinaccordancewiththe current fiowing from said main generator through said helper drive motor. and suction-responsive control means connected with said other control field winding for exciting it in accordance with variationsinsuction vacuumsoastocausean increase in torque oi said helper drive motor at decreasingvacuum.

6..4nelectric drive iorsuctionscotionoia paper machine. comprising a main roll drive. a direct-current helper drive motor. a main generator having an armature series-connected with said helper drive motor and having two cumulative field windings. a bridge circuit having {our serially interconnected branches and tour terminal points intermediate said branches. said bridge circuit including said two field windinll i two opposite ones or said branches. a pilot generatordesignedtobeoperated irom saldmain drive and being connected across two opposite ones oi said terminal points, a regulating generator having an armature connected across said two other terminal points and having two control field windings or mutually opposing action. one

oi said control field windings being connected to said main generator and said helper drive motor so as to be excited in accordance with the current fiowing from said main generator through said helper drive motor. and suction-responsive control means connected with said other control field winding or exciting it in accordance with variations in suction vacuum. whereby said helperf drive motor is controlled to increase its torque atdecreasing vacuum.

RIB! R. BAKER, WALTER R. HARRIS.

BII'BINCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

